The long term goal is to advance our understanding of the mechanisms involved in long-range electron transfer reactions, and in charge- separation and stabilization in proteins. Photosynthetic bacterial reaction centers from Rhodopseudomonas viridis and Rhodobacter sphaeroides are the proteins chosen for the study because they offer several experimental opportunities that are unique; they also present an area of ignorance regarding what is the basis for the free-energies of the various electron transfer steps in the reaction center and their forward and reverse kinetics that define the final quantum and energetic efficiencies. The present proposal is focused mainly on the role of nuclear motions of reacting cofactors and/or protein matrix in governing reaction rates and the relationships of the rate to the driving force. The possibility of detecting and measuring the effects of intervening virtual states in superexchange with reactants and products will be addressed in particular with regard to the primary charge separation. The experiments will measure the rates from 300 to 1K of several key reactions that involve chlorophylls, pheophytins, quinones and hemes associated with the reaction center. The reactions occur in the pico- to millisecond range. The novel point of the work is that the measurements will be done on reaction centers in which the free-energy of some of the reactions are altered by as much as 1 eV by application of electric fields across monolayer films of reaction centers and by chemical replacement. Efforts will also be made to examine the feasibility of initiating electron transfer in the dark by electric field jumps. The results should provide basic and general knowledge about reorganization energies and the frequencies of cofactor/protein medium modes that are coupled to biological electron transfer. The results should be of relevance to the contemporary electron transfer theories for which this kind of data is badly needed. Progress into understanding the mechanism of action of reaction centers from bacteria will, as in the past, impact on analogous plant photosystems and related charge separating respiratory membrane proteins, as well as on efforts of chemists to synthesize molecules that function similarly.